This invention relates to novel low density compositions having utility for instance as thermal or sound insulating masses as well as fire-proofing coatings for structural steel, etc. The invention more particularly concerns low density compositions produced by hydrating essentially mixtures of inorganic settable binders and a novel lightweight aggregate obtained from combusting essentially the bark obtained as a waste by-product in the processing of logs into useful materials, e.g. pulp for paper products, etc.
Hydratable mixtures of inorganic binders such as gypsum plaster and Portland cement with lightweight open or porous aggregate materials such as expanded vermiculite, expanded perlite, expanded clay, etc. have been used extensively as thermal insulating and fireproofing compositions. Water is added to the mixtures and the wet mix allowed to hydrate or set. The lightweight porous aggregate imparts the desired low density and porosity to the set masses which typically have dry densities of less than about 45, more often less than about 30 pounds per cubic foot. The lowest densities are conventionally obtained by incorporating air into the wet mixtures typically with the assistance of surfactants or foaming agents added to the compositions. The desirability of further including for some applications foam-stabilizing agents, strength-enhancing fibers, etc., is well established in the art.
Practical use of such low density cementitious products as thermal insulating and fireproofing masses often requires that the wet mixtures be pumped distances and thereafter poured or spray-applied. In the use for example of such materials as a lightweight insulating layer in roof decks of commercial buildings, the material typically is mixed at ground level and thereafter pumped vertically to the roof deck. After placement in this fashion, the compositions after hydration must exhibit the desired low density, typically in the range of about 20 to 30 pounds per cubic foot. In similar fashion, low density compositions for fireproofing for example steel structural beams of buildings are mixed, pumped great distances and thereafter sprayed onto the exposed beams. Typical dry densities of hydrated cement/lightweight aggregate fireproofings applied in this manner lie in the range of about 10 to about 25 pounds per cubic foot. There is a continuing need for economic aggregate materials which in particulate form are light in weight and open or porous, yet are sufficiently firm and rigid to withstand compaction by, for example, the extensive mixing and pumping operations required on a large commercial scale.